Buy enough mulch without burying the bed
The most useful mulch number is the fresh depth needed today. Existing mulch and excluded spaces matter as much as the outside dimensions. Whole-bag rounding changes your purchase, but it should not change the depth you spread.
Updated October 6, 2026 · Original YardTotals calculation exercise · Methods & corrections
Choose the total depth, then subtract what is there
For trees and shrubs, University of Maryland Extension describes a 2–3 inch mulch layer and keeping mulch away from trunks. That is total depth, not an annual addition. Check advice for your plants and material, measure the existing layer at several points, and enter only the positive difference. A bed already at its target depth needs no extra volume.
Separate thin patches from bare patches
In this worked exercise, Bed A is 14 × 5 ft and already has 2 inches of mulch; its chosen target is 3 inches. It needs 1 new inch. Bed B is 9 × 4 ft and is bare; its chosen target is 2 inches. It needs 2 inches. Enter each as a separate area. Do not enter the full target of 3 inches for Bed A: that would triple its fresh material estimate.
Add first, round bags last
Bed A needs 5.833 ft³ and Bed B needs 6 ft³, totaling 11.833 ft³. With a chosen 5% allowance, that becomes 12.425 ft³, or 0.460 yd³. Seven 2-ft³ bags supply 14 ft³; five 3-ft³ bags supply 15 ft³. Both exceed the estimate, but the larger bag is not automatically the cheaper purchase. Use the actual label volume and price.
Treat surplus as a purchase consequence
The seven smaller bags leave 1.575 ft³ above the estimate with allowance. The five larger bags leave 2.575 ft³. This extra volume comes from buying whole packages. It is not a reason to spread the beds deeper or pile mulch against bark. Keep unused material for another appropriate area.
Decide between bags and a loose delivery
For a requirement below half a yard, a one-yard bulk minimum can create much more surplus than bags. Enter the calculated requirement in the bags-versus-bulk worksheet, then use the supplier’s actual minimum and delivery charge. Compare product type and quality too. The lowest total may still be inconvenient if there is no suitable drop spot or a long wheelbarrow route.
Exclude spaces that will remain uncovered
For a bed containing paving or an unmulched center, subtract that area before entering Known area. A circle’s diameter runs all the way across the center; it is twice its radius. For a ring, subtract the inner circle from the outer circle using the measuring guide, then enter the resulting area and the fresh depth.
| Section | Fresh depth | Measured volume |
|---|---|---|
| Bed A: 14 × 5 ft | 3 in target − 2 in existing = 1 in | 5.833 ft³ |
| Bed B: 9 × 4 ft | 2 in target − 0 in existing = 2 in | 6 ft³ |
| Combined with 5% | Apply allowance once | 12.425 ft³ / 0.460 yd³ |
| Purchase options | 2-ft³ bags / 3-ft³ bags | 7 bags / 5 bags |
Source for tree and shrub placement: University of Maryland Extension. The bed sizes, bag sizes and arithmetic above are our illustrative exercise. Read the source ↗
Before placing the order
- Have you subtracted the existing mulch layer?
- Are trunks, paving and unmulched patches excluded?
- Does the bag size match the product label?
- Can surplus be stored instead of adding excessive depth?